In the absorption/desorption process, a hydrogen mass flow
rate of 1[NL/min] is maintained when filling or emptying the
tank, and the characterization starts from the initial conditions
of ambient temperature and a tank that is either full or
empty. The flow rate is deliberately kept low in order to avoid
high kinetics and to limit hydride temperature variations. A
specific amount of hydrogen mass is also controlled, and a
pause of 30 s is observed during the process after each packet
of 0.5 g.
In the case of absorption, by imposing the hydrogen mass
flow rate, the hydride undergoes a volume expansion
(compression) and then it changes to another state. The
pressure increases from P(i) to P(i þ 1) with (P(i þ 1) > P(i)). The
pressure change and the exothermic absorption process cause
the temperature in the tank to increase. The pressure and
temperature will rise until the temperature reaches apredefined level, controlled via the software interface. Once
both the temperature threshold and the amount of hydrogen
are reached, the filling of the tank is stopped. By convection,
the system returns naturally to the ambient temperature
regulated in the climatic chamber. At this equilibrium temperature,
data relating to pressure and capacity are recorded
as part of the PCT curve. This process is repeated throughout
the complete absorption stage, up to the maximum operating
tank pressure level. The capacity at point i can then be written:
During the absorption